Senior journalists at the Sun are preparing to launch a legal challenge to the News Corporation unit that disclosed confidential sources to the police, leading to the arrest of nine of the paper's current and former staff this month.

Journalists at the News International red-top have approached the National Union of Journalists with a view to hiring the leading human rights lawyer, Geoffrey Robertson QC, to question the legality of parent company News Corp's management and standards committee.

The NUJ has been contacted by more than a dozen journalists from the Sun with concerns about the protection of sources, it is understood.

The potential legal challenge represents a dramatic new front in the civil war at Rupert Murdoch's Wapping newspaper headquarters on the eve of his arrival in London to deal with the crisis at the Sun.

The leading lawyer, who has fought on behalf of publishers for press freedom throughout his career, suggested in the column that News Corp's MSC should "be required to learn by heart" a passage from the European court of human rights' ruling in the case of Goodwin v UK, which predates the Human Rights Act and affirms the importance of protection for journalists' sources.

This passage states: "Protection of journalistic sources is one of the basic conditions for press freedom... without such protection, sources may be deterred from assisting the press in informing the public on matters of public interest.

"As a result the vital public watchdog role of the press may be undermined and the ability of the press to provide accurate and reliable information may be adversely affected."

Robertson had not been formally approached by the NUJ at the time of publication.

The NUJ has signed up a number of Sun journalists as new members since the arrest of five of the newspaper's senior journalists on Saturday, it is understood.

Michelle Stanistreet, general secretary of the NUJ, is due to meet lawyers on Wednesday about a challenge to News Corp's MSC.

Stanistreet said on Wednesday that "Sun journalists have approached the NUJ with concerns about sources being compromised."

Michelle Stanistreet, NUJ general secretary, said: "We have been approached by a group of journalists from the Sun. We are now exploring a number of ways to support them, including discussing legal redress.

"We recognise that [News International Staff Association] officials are trying their best for staff, but they have no chance because they are seen as creatures of Rupert Murdoch's management. The NUJ can defend staff at the Sun, and elsewhere in News International, and represent them against a management that seems prepared to throw them to the wolves. It is not an exaggeration to say that if journalists are not allowed to offer protection to their sources – often brave people who are raising their heads above the parapet to disclose information – then the free press in the UK is dead.

"The protection of sources is an essential principle which has been repeatedly reaffirmed by the European Court of Human Rights as the cornerstone of press freedom and the NUJ shall defend it. In 2007 a judge made it clear that journalists and their sources are protected under article 10 of the Human Rights Act and it applies to leaked material.

"I will be writing to News Corp's management and standards committee asking what authority it had to disclose this information. I will also be writing to staff at News International to invite them to join the NUJ."

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